The present invention relates to a mechanical seal, and more particularly to a mechanical seal disposed between two relatively moving bearing surfaces such as, for example, between a rotating bearing surface and an associated stationary bearing surface for providing a seal around the drive shaft of a variable displacement swash plate type compressor used in an air conditioning system for a vehicle.
A mechanical face seal is frequently used in an automotive cooling pump or refrigeration compressor. Generally, such seals include a stationary annular bearing surface integral with the compressor housing and an associated sealing ring disposed on a rotating drive shaft. A means are provided for urging the facing surfaces of the stationary bearing surface and the sealing ring together. The rotating surface of the sealing ring contacts the stationary bearing surface to form a sealing face which is perpendicular to the shaft. The stationary sealing surface is typically formed of cast iron, stainless steel, ceramic, hard chromium-plated steel or hardened bearing steel; and the associated rotating ring is formed of sintered carbon-graphite, resin-bonded carbon-graphite, resin impregnated carbon-graphite or ceramic.
Refrigeration compressors are used to compress refrigerants, such as carbon dioxide, as part of a standard vapor-compression refrigeration cycle. Typically, a gaseous refrigerant is mixed with a liquid lubricating medium, such as oil, before entering the compressor. The oil is employed to lubricate the compressor components, such as bearings and seals, to reduce component wear. Refrigeration compressors typically include a shaft rotatably supported by bearings within a compressor housing. Mechanical seals are typically employed in such refrigeration compressors to inhibit leakage of lubricating oil between the compressor housing and the shaft.
When a mechanical seal is mounted in a conventional variable displacement swash plate type compressor of an air-conditioner for a vehicle in which carbon dioxide refrigerant is used, the operational conditions of the mechanical seal become severe. The pressure within such a compressor is greater than within a compressor using a different refrigerant, resulting in a greater axial sealing force on the mechanical seal. Additionally, conventional lubricating oil is not soluble in carbon dioxide and therefore the lubricating oil cannot be efficiently distributed within the compressor. Such inefficient distribution of lubricating oil can cause the sealing face of the mechanical seal to receive an insufficient amount of lubricating oil. Insufficient lubrication will cause excessive friction in the sealing face, resulting in over-heating and failure of the mechanical seal.
The mechanical seals of the prior art rely primarily on the flow of oil mixed with refrigerant gas to effect proper lubrication. Therefore, ineffective lubrication of the sealing face occurs due the lack of consistent flow of refrigerant gas within the compressor.
It would be desirable to produce a mechanical seal wherein a constant supply of lubrication is released into the sealing face to result in improved lubrication of the mechanical seal.
Consistent and consonant with the present invention, a mechanical seal wherein a constant supply of lubrication is released into the sealing face to result in improved lubrication of the mechanical seal has surprisingly been discovered.
The shaft mounted mechanical seal for two relatively moving bearing surfaces comprises:
a shaft having a stepped outer surface and a radially outwardly extending shoulder formed on the outer surface;
a first bearing surface formed on one of a rotatable annular element and a stationary annular element, the rotatable annular element adapted to rotate with the shaft and the stationary element adapted to militate against rotation with the shaft;
a second bearing surface formed on the other of the rotatable annular element and the stationary annular element, the second bearing surface being in juxtaposed relation to the first bearing surface;
an annular retainer disposed on the outer surface of the shaft and abutting the shoulder of the shaft, the retainer having one section for fixedly retaining the rotatable annular element on the outer surface of the drive shaft;
a spring member disposed between the retainer and the rotatable annular element for urging the rotatable annular element towards the stationary annular element to engage the first bearing surface and the second bearing surface;
a groove formed in at least one of the first bearing surface and the second bearing surface; and
a dry lubricant disposed in the groove to provide lubrication between the first bearing surface and the second bearing surface.